Get familiar with diatonic harmony / chord scales if you're not already. When I'm practicing with a big band, I also find it useful to run the chart on my own using chord tones only, just in case i'm called on to solo. Then I have some ideas up my sleeve rather than just jumping into my trick bag!!
I also like to practice horn lines - especially Charlie Parker - to get phrasing ideas. I got this idea years ago from John Patitucci, who offered that advice in all his interviews
There are a lot of good books on improvising, check out Ed Friedland's Bass Improvisation or http://www.shermusic.com/new/0961470100.shtml
I've recently got some great ideas from this guy: http://youtu.be/QA3eSm5uTUY